Estrogen is a powerful neuroprotective hormone that is particularly effective in reducing cerebral ischemic damage in stroke. Endogenous and exogenous estrogen is also associated with protection from neurodegenerative disease in humans. However, the benefits of estrogen are mitigated by recent clinical results suggesting that hormone replacement therapy (HRT) has health consequences. Concerns about hormone dependent cancer will continue to deter women from taking replacement therapy. Pharmacological selective estrogen receptor modulators (SERMs) show promise in preserving the beneficial effects of estrogen without increasing cancer risk. However, many women are already opting for "natural" SERMs such as plant derivatives containing soy and other phytoestrogens with the presumption that such therapies are both effective and safer than HRT. Epidemiological and experimental data suggest that diets high in soy phytoestrogens provide many of the same benefits as estrogen with the potential for decreased negative side effects seen with traditional HRT. Nevertheless, very little is known about the effects of dietary soy phytoestrogens in the brain. In vitro, soy phytoestrogens can mimic some of estrogen's neuroprotective actions, but these same compounds have also been shown to inhibit some estrogen actions in the brain. The present proposal seeks to determine the whether of soy phytoestrogens protect neurons from ischemic damage in vitro and in vivo. We hypothesize that physiologically relevant doses of soy phytoestrogens are neuroprotective by mimicking both genomic and non-genomic actions of estrogen. Aim 1 will test the hypothesis that the soy phytoestrogens genestein, daidzein, and equol inhibit apoptotic cell death in neuronal cell line models of cerebral ischemia in an estrogen receptor-dependent manner. Aim 2 will test the hypothesis that in the absence of endogenous estrogen a high soy diet will decrease infarct size and cell death associated with middle cerebral artery occlusion in rats. Aim 3 will test the hypothesis that in the absence of endogenous estrogen, ingestion of a high soy diet will induce the expression of the neuroprotective genes BDNF, NGF, Bcl-2, BCl-xL, and TrkB and reduce expression of the pro-apoptotic p75 NTR in brain regions damaged by middle cerebral artery occlusion. This proposal seeks to provide critical new information about the ability of phytoestrogens to protect the brain from focal cerebral ischemia.